Electromagnetic switch device

ABSTRACT

Disclosed is an electromagnetic switch device for star-delta connections including a body, three power terminals respectively connected to three-phase power lines at one side of the body, three main starting terminals respectively connected to one-side terminals of a three-phase electric motor at the other side of the body, three star-delta terminals respectively connected to the other-side ends of the three-phase electric motor at the other side of the body, an electromagnet for a main circuit and an electromagnet for star-delta connections disposed at a lower portion of the body in such a fashion that they are laterally aligned with each other, each of the electromagnets including a fixed core and a coil wound around the fixed core, a main circuit switching unit serving to selectively connect each of the main starting terminals to an associated one of the power terminals in accordance with a magnetization of the main circuit-end electromagnet, and a star-delta connection switching unit serving to selectively connect the star-delta terminals to one another or to the main starting terminals, respectively, in accordance with a magnetization of the star-delta connection-end electromagnet.

TECHNICAL FIELD

The present invention relates to a magnetic contactor(electromagneticswitch device) for star-delta connections, and more particularly to anelectromagnetic switch device designed to be used for a star-deltastarter adapted to start up a three-phase electric motor in order toallow the motor to be driven at its full speed within a short period oftime.

BACKGROUND ART

As well known, star (Y)-delta (Δ) starters, which are used to start upan electric motor, serve to establish a star connection for the electricmotor upon the start-up of the electric motor, thereby reducing startingcurrent and starting torque required in the start-up of the electricmotor to a ⅓ level, while switching the connection for the electricmotor into a delta connection after completion of the-start-up of theelectric motor so that the electric motor is driven-in the deltaconnection state. Such star-delta starters are widely used in a varietyof industrial fields in order to protect electric motors and peripheraldevices thereof from overload.

Star-delta starters are classified into a contact type using anelectromagnetic switch device adapted to switch electric contacts by useof electromagnets, and a non-contact type using a semiconductor switchdevice. The type using an electromagnetic switch device is more widelyused.

FIGS. 1a, 1 b and 2 illustrate a conventional electromagnetic switchdevice and a star-delta starter using the electromagnetic switch device,respectively. FIG. 1a is a perspective view illustrating theelectromagnetic switch device, and FIG. 1b is a cross-sectional viewtaken along the line A—A of FIG. 1a. FIG. 2 is an equivalent circuitdiagram illustrating the star-delta starter.

As shown in FIGS. 1a and 1 b, the conventional electromagnetic switchdevice, which is denoted by the reference character C, includes a body1, and a cover 2 separably attached to an upper surface 1 a of the body1. Three pairs of terminals 3 are disposed on the upper surface 1 a ofthe body 1 in such a fashion that the terminals of each terminal pairare arranged at opposite sides of the body 1, respectively, while beinginsulated from one another. Electric power lines not shown are connectedto the terminals 3, respectively. Isolating plates 4 are arranged atopposite sides of the cover 2 to isolate adjacent ones of the terminals3.

Three pairs of fixed contacts 5 are also provided. Each fixed contact 5is arranged at an end of an associated one of the terminals 3 extendingtoward a central portion of the body 1. The fixed contacts 5 areinsulated from one another. A vertical moving member 6 is arranged atthe central portion of the body 1 in such a fashion that it is upwardlyand downwardly movable. Three pairs of moving contacts 7 insulated fromone another are mounted to the vertical moving member 6 at oppositesides of the vertical moving member 6 in such a fashion that each ofthe, moving contacts 7 selectively comes into contact with an associatedone of the fixed contacts 5 so that it is short-circuited or opened withrespect to the associated fixed contact 5. A compression coil spring 8is arranged around the vertical moving member 6 between the uppersurface 1 a of the body 1 and the moving contacts 7 in such a fashionthat it always urges the vertical moving member 6 upwardly.

A fixed core 9 is arranged at a lower portion of the body 1. A coil 10is wound around the fixed core 9 in order to form an electromagnet.Above the fixed core 9, a moving core 11 is arranged in such a fashionthat it moves vertically along with the vertical moving member 6 inaccordance with a magnetization of the electromagnet.

The conventional star-delta starter using electromagnetic switch deviceshaving the above mentioned configuration includes an electromagneticswitch device C1 for a main circuit, an electromagnetic switch device C2for a star circuit, and an electromagnetic switch device C3 for a deltaconnection, which are connected together as shown in the equivalentcircuit diagram, of FIG. 2 and activated by a timer (not shown) to startup a three-phase electric motor M.

When current flows through the coil 10 of the electromagnetic switchdevice C2 for the star circuit upon starting the three-phase electricmotor M, the electromagnet formed by the fixed core 9 and coil 10 ismagnetized by virtue of the current.

Accordingly, the electromagnet generates a magnetic force greater thanthe resilience of the spring 8, so that the vertical moving member 6 andmoving core 11 are downwardly moved. As a result, the moving contacts 7,which also move downwardly, come into contact with the fixed contacts 5,respectively.

When the electromagnetic switch device C1 for the main circuit isactivated in accordance with the same procedure as mentioned above, astar connection is established for the three-phase electric motor M, sothat the three-phase electric motor is started up using starting currentand starting torque reduced to a ⅓ level. At the same time, the timernot shown begins to operate in order to count the drive time of thethree-phase electric motor M.

After a predetermined period of time elapses, the current flowingthrough the coil 10 of the electromagnetic switch device C2 for the starconnection is cut off by an operation of the timer. At the same time,current flows through the coil 10 of the electromagnetic switch deviceC3 for the delta connection.

In this state, the magnetic force of the electromagnet formed by thefixed core 9 and coil 10 of the electromagnetic switch device C2 for thestar connection disappears. As a result, the vertical moving member 6 isupwardly moved along with the moving core 11 and moving contacts 7 byvirtue of the resilience of the spring 8, thereby causing the movingcontacts 7 to be separated from the fixed contacts 5.

Meanwhile, the electromagnet formed by the fixed core 9 and coil 10 ofthe electromagnetic switch device C3 for the delta connection ismagnetized by virtue of the current flowing through the coil 10. As aresult, the moving contacts 7 are downwardly moved, so that they comeinto contact with the fixed contacts 5, respectively.

Accordingly, the electromagnetic switch device C3 for the deltaconnection is short-circuited to electric power lines at its one-sideterminals 3. As a result, the three-phase electric motor M is switchedto the star connection state to a delta connection state, so that it isdriven at a full speed.

In the star-delta starter having the above mentioned configuration, eachof its electromagnetic switch devices is used only for a single purpose,that is, a star connection or a delta connection. For this reason, theconventional star-delta starter cannot implement a desired system unlessat least two electromagnetic switch devices are used, even when thoseused for the main circuit are not taken into consideration.

As a result, the conventional star-delta starter involveshigh-manufacturing and installing costs and a large occupation space.

The conventional star-delta starter also involves a complex wiring forthe connection between the electric motor and the electromagnetic switchdevice used. Such a complex wiring may result in a possibility oferroneous connections. In particular, such a wiring may be easilydamaged by an external force applied thereto, thereby resulting in anerroneous operation of the starter or a damage of the electric motor.

DISCLOSURE OF INVENTION

Therefore, an object of the invention is to solve the above mentionedproblems involved in the prior art, and to provide an electromagneticswitch device for star-delta connections which includes twoelectromagnets arranged in its body and two switching units operating inaccordance with respective magnetization states of the electromagnets inorder to selectively establish a star connection or a delta connectionfor a three-phase electric motor, so that it can reduce installationcosts and an occupation space when it is applied to a star-delta starterwhile using no unnecessary wiring, thereby reducing erroneousconnections and erroneous operations.

In accordance with the present invention, this object is accomplished byproviding an electromagnetic switch device for star-delta connectionscomprising: a body; three power terminals arranged at one side of thebody and respectively connected to three-phase power lines, the powerterminals being insulated from one another; three main startingterminals arranged at the other side of the body and respectivelyconnected to one-side terminals of a three-phase electric motor, themain starting terminals being insulated from one another; threestar-delta terminals arranged at the other side of the body outside themain starting terminals and connected to the other-side ends of thethree-phase electric motor, respectively, the star-delta terminals beinginsulated from one another; an electromagnet for a main circuit and anelectromagnet for star-delta connections disposed at a lower portion ofthe body in such a fashion that they are laterally aligned with eachother while being insulated from each other, each of the electromagnetsincluding a fixed core and a coil wound around the fixed core; a maincircuit switching unit arranged near the main circuit-end electromagnetin the interior of the body, the main circuit switching unit serving toselectively connect each of the main starting terminals to an associatedone of the power terminals in accordance with a magnetization of themain circuit-end electromagnet; and a star-delta connection switchingunit arranged near the star-delta connection-end electromagnet in theinterior of the body, the star-delta connection switching unit servingto selectively connect the star-delta terminals to one another or to themain starting terminals, respectively, in accordance with amagnetization of the star-delta connection-end electromagnet.

Preferably, the electromagnetic switch device further comprises a timerarranged in the interior of the body and adapted to count an activationtime of the main circuit-end electromagnet, thereby determining a pointof time when the star-delta connection-end electromagnet is to beactivated.

The electromagnetic switch device may further comprise isolating platesarranged between adjacent ones of the power terminals, between adjacentones of the main starting terminals, and between adjacent ones of thestar-delta terminals to isolate the adjacent power terminals, theadjacent main starting terminals, and the adjacent star-delta terminals,respectively.

The main circuit switching unit may comprise: a moving core verticallymovable in accordance with a magnetization of the main circuit-endelectromagnet; a vertical moving member integrally coupled to the movingcore in such a fashion that it is moved along with the moving core;three pairs of fixed contacts arranged at desired positions within avertical movement zone of the vertical moving member in such a fashionthat the fixed contacts included in each of the fixed contact pairs aredisposed at opposite sides of the vertical moving member, respectively,the fixed contacts arranged at one side of the vertical moving memberbeing connected to the power terminals, respectively, while beinginsulated from one another, and the fixed contacts arranged at the otherside of the vertical moving member being connected to the main startingterminals, respectively, while being insulated from one another; andthree pairs of moving contacts mounted to the vertical moving member insuch a fashion that the moving contacts included in each of the movingcontact pairs are disposed at opposite sides of the vertical movingmember, respectively, the moving contacts arranged at one side of thevertical moving member being insulated from one another, the movingcontacts arranged at the other side of the vertical moving member beinginsulated from one another, and the moving contacts being verticallymoved in accordance with a vertical movement of the vertical movingmember, so that they selectively come into contact with respectiveassociated ones of the fixed contacts, thereby causing the powerterminal-end fixed contacts to be selectively connected to the startingterminal-end fixed contacts.

The star-delta connection switching unit may comprise: a moving corevertically movable in accordance with a magnetization of the star-deltaconnection-end electromagnet; a vertical moving member integrallycoupled to the moving core in such a fashion that it is moved along withthe moving core; three pairs of fixed contacts for star-delta connectionarranged at desired positions within a vertical movement zone of thevertical moving member in such a fashion that the fixed contactsincluded in each of the fixed contact pairs are disposed at oppositesides of the vertical moving member, respectively, the fixed contactsarranged at one side of the vertical moving member being connected tothe main starting terminals, respectively, while being insulated fromone another, and the fixed contacts arranged at the other side of thevertical moving member being connected to the star-delta terminals,respectively, while being insulated from one another; three pairs ofmoving contacts for delta connection mounted to the vertical movingmember in such a fashion that the moving contacts included in each ofthe moving contact pairs are disposed at opposite Sides of the verticalmoving member, respectively, the moving contacts arranged at one side ofthe vertical moving member being insulated from one another, the movingcontacts arranged at the other side of the vertical moving member beinginsulated from one another, and the moving contacts being verticallymoved in accordance with a vertical movement of the vertical movingmember, so that they selectively come into contact with respectiveassociated ones of the fixed contacts, thereby causing the star-deltaconnection-end fixed contacts to be selectively connected to thestarting terminal-end fixed contacts so as to achieve a deltaconnection; and three moving contacts for star connection mounted to thevertical moving member at a position vertically shifted from the deltaconnection-end moving contacts near the star-delta connection-end fixedcontacts, the star connection-end moving contacts being short-circuitedtogether, and the star connection-end moving contacts being verticallymoved in accordance with a vertical movement of the vertical movingmember, so that they selectively come into contact with respectiveassociated ones of the fixed contacts, thereby causing the fixedcontacts to be selectively connected together so as to achieve a starconnection, the star connection by the star connection-end movingcontacts being achieved when the delta connection by the deltaconnection-end moving contacts is released.

Each of the main circuit switching unit and star-delta connectionswitching unit may further comprise a return springs adapted to providea return force for returning the associated vertical moving member to anoriginal position thereof at which the associated moving contacts areseparated from respective associated ones of the fixed contacts.

Each of the main circuit switching unit and star-delta connectionswitching unit may further comprise an arc prevention spring arranged inthe associated vertical moving member and adapted to always urge theassociated moving contacts toward the associated fixed contacts, therebyincreasing the contact force of the moving contacts when the movingcontacts come into contact with the fixed contacts, so as to suppressgeneration of arc at regions where the moving contacts come into contactwith the fixed contacts, respectively.

BRIEF DESCRIPTION OF DRAWINGS

The above objects, and other features and advantages of the presentinvention will become more apparent after a reading of the followingdetailed description when taken in conjunction with the drawings, inwhich:

FIGS. 1a, 1 b and 2 illustrate a conventional electromagnetic switchdevice and a star-delta starter using the electromagnetic switch device,respectively, wherein FIG. 1a is a perspective view illustrating theelectromagnetic switch device, FIG. 1b is a cross-sectional view takenalong the line A—A of FIG. 1a, and FIG. 2 is an equivalent circuitdiagram illustrating the star-delta starter; and

FIGS. 3a, 3 b and 4 illustrate an electromagnetic switch deviceaccording to the present invention and a star-delta starter u usitheelectromagnetic switch device, respectively, wherein FIG. 3a is aperspective view illustrating the electromagnetic switch device, FIG. 3bis a cross-sectional view taken along the line A—A of FIG. 3a, and FIG.4 is an equivalent circuit diagram illustrating the star-delta starterusing the electromagnetic switch device according to the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 3a, 3 b and 4 illustrate an electromagnetic switch deviceaccording to the present invention and a star-delta starter using theelectromagnetic switch device, respectively. FIG. 3a is a perspectiveview of the electromagnetic switch device, and FIG. 3b is across-sectional view taken-along the line A—A of FIG. 3a. FIG. 4 is anequivalent circuit diagram of the star-delta starter using theelectromagnetic switch device according to the present invention.

As shown in FIGS. 3a and 3 b, the electromagnetic switch device of thepresent invention, which is denoted by the reference character C,includes a body 110, and three power terminals 121 a, 121 b, and 121 carranged at one side of the body 110 and respectively connected tothree-phase power lines R, S, and T. The power terminals 121 a, 121 b,and 121 c are insulated from one another. The electromagnetic switchdevice also includes three main starting terminals 122 a, 122 b, and 122carranged at the other side of the body 110 and respectively connectedto one-side terminals u, v, and w of a three-phase electric motor M. Themain starting terminals 122 a, 122 b, and 122 c are insulated from oneanother. Three star-delta terminals 123 a, 123 b, and 123 c are arrangedat the other side of the body 110 outside the main starting terminals122 a to 122 c. The star-delta terminals 123 a, 123 b, and 123 c areconnected to the other-side ends Z, X, and Y of the three-phase electricmotor M, respectively. The star-delta terminals 123 a, 123 b, and 123 care insulated from one another.

An electromagnet 130 for a main circuit and an electromagnet 140 forstar-delta connections are disposed at a lower portion of the body 110in such a fashion that they are laterally aligned with each other whilebeing insulated from each other. The electromagnet 130 includes a fixedcore 131 and a coil 132 whereas the electromagnet 140 includes a fixedcore 141 and a coil 142.

The electromagnetic switch device also includes a main circuit switchingunit 150 arranged above the main circuit-end electromagnet 130 in theinterior of the body 110. The main circuit switching unit 150 serves toselectively connect the main starting terminals 122 a, 122 b, and 122 cto respective power terminals 121 a, 121 b, and 121 c in accordance witha magnetization of the main circuit-end electromagnet 130.

The main circuit switching unit 150 includes a main circuit-end movingcore 151 and a main circuit-end vertical moving member 152 integrallycoupled together and arranged above the main circuit-end electromagnet130 near the main circuit-end electromagnet 130. The moving core 151 andvertical moving member 152 are adapted to be moved together inaccordance with a magnetization of the electromagnet 130. The maincircuit switching unit 150 also includes three pairs of main circuit-endfixed contacts 153 a, 153 b, and 153 c arranged at desired positionswithin a vertical movement zone of the main circuit-end vertical movingmember 152 in such a fashion that the fixed contacts of each fixedcontact pair are disposed at opposite sides of the vertical movingmember 152, respectively. The fixed contacts 153 a, 153 b, and 153 carranged at one side of the vertical moving member 152 are connected tothe power terminals 121 a, 121 b, and 121 c, respectively, while beinginsulated from one another. The fixed contacts 153 a, 153 b, and 153 carranged at the other side of the vertical moving member 152 areconnected to the main starting terminals 122 a, 122 b, and 122 c,respectively, while being insulated from one another. Three pairs ofmoving contacts 154 a, 154 b, and 154 c are mounted to the maincircuit-end vertical moving member 152 in such a fashion that the movingcontacts of each moving contact pair are disposed at opposite sides ofthe vertical moving member 152, respectively. The moving contacts 154 a,154 b, and 154 c arranged at one side of the vertical moving member 152are insulated from one another. In similar, the moving contacts 154 a,154 b, and 154 c arranged at the other side of the vertical movingmember 152 are insulated from one another. The moving contacts 154 a,154 b, and 154 c are vertically moved in accordance with a verticalmovement of the vertical moving member 152, so that they selectivelycome into contact with respective associated ones of the fixed contacts153 a, 153 b, and 153 c, thereby causing the power terminal-end fixedcontacts 153 a, 153 b, and 153 c to be selectively connected to thestarting terminal-end fixed contacts 153 a, 153 b, and 153 c.

Return springs 155 are arranged around the moving core 151 between theupper surface of the main circuit-end electromagnet 130 and the lowersurface of the main circuit-end vertical moving member 152 in order toprovide a return force for returning the vertical moving member 152 toits original position at which the moving contacts 154 a, 154 b, and 154c are separated from respective associated ones of the fixed contacts153 a, 153 b, and 153 c. An arc prevention spring 156 is arranged in themain circuit-end vertical moving member 152 in order to always urge themoving contacts 154 a, 154 b, and 154 c toward the fixed contacts 153 a,153 b, and 153 c, thereby increasing the contact force of the movingcontacts 154 a, 154 b, and 154 c when the moving contacts 154 a, 154 b,and 154 c come into contact with the fixed contacts 153 a, 153 b, and153 c, so as to suppress generation of arc at those contacts.

The electromagnetic switch device further includes a star-deltaconnection switching unit 160 arranged above the star-deltaconnection-end electromagnet 140 in the interior of the body 110. Thestar-delta connection switching unit 160 serves to selectively connectthe star-delta terminals 123 a, 123 b, 123 cto one another or torespective main starting terminals 122 a, 122 b, and 122 c in accordancewith a magnetization of the star-delta connection-end electromagnet 140.

The star-delta connection switching unit 160 includes a star-deltaconnection-end moving core 161 and a star-delta connection-end verticalmoving member 162 integrally coupled together and arranged above thestar-delta connection-end electromagnet 140 near the star-deltaconnection-end electromagnet 140. The moving core 161 and vertical,moving member 162 are adapted to be moved together in accordance with amagnetization of the electromagnet 140. The star-delta connectionswitching unit 160 also includes three pairs of fixed contacts 163 a,163 b, and 163 c for star-delta connection arranged at desired positionswithin a vertical movement zone of the star-delta connection-endvertical moving member 162 in such a fashion that the fixed contacts ofeach fixed contact pair are disposed at opposite sides of the verticalmoving member 162, respectively. The fixed contacts 163 a, 163 b, and163(0 163 c . ranged at one side of the vertical moving member 162 areconnected to the main starting terminals 122 a, 122 b, and 122 c,respectively, while being insulated from one another. The fixed contacts163 a, 163 b, and 163 c arranged at the other side of the verticalmoving member 162 are connected to the star-delta terminals 123 a, 123b, and 123 c, respectively, while being insulated from one another.Three pairs of moving contacts 164 a, 164 b, and 164 c for deltaconnection are mounted to the star-delta connection-end vertical movingmember 162 in such a fashion that the moving contacts of each movingcontact pair are disposed at opposite sides of the vertical movingmember 162, respectively. The moving contacts 164 a, 164 b, and 164 carranged at one side of the vertical moving member 162 are insulatedfrom one another. In similar, the moving contacts 164 a, 164 b, and 164c arranged at the other side of the vertical moving member 162 areinsulated from one another. The moving contacts 164 a, 164 b, and 164 care vertically moved in accordance with a vertical movement of thevertical moving member 162, so that they selectively come into contactwith respective associated ones of the fixed contacts 163 a, 163 b, and163 c, thereby causing the star-delta connection-end fixed contacts 163a, 163 b, and 163 c to be selectively connected to the startingterminal-end fixed contacts 163 a, 163 b, and 163 c.

Three moving contacts 167 a, 167 b, and 167 c for star connection arealso mounted to the star-delta connection-end vertical moving member 162above the delta connection-end moving contacts 164 a, 164 b, and 164 cnear the fixed contacts 163 a, 163 b, and 163 c connected to th ther-delta terminals 123 a, 123 b, and 123 c. The star connection-endmoving contacts 167 a, 167 b, and 167 c are short-circuited together.The moving contacts 167 a, 167 b, and 167 c are vertically moved inaccordance with a vertical movement of the vertical moving member 162,so that they selectively come into contact with respective associatedones of the fixed contacts 163 a, 163 b, and 163 c, thereby causing thefixed contacts 163 a, 163 b, and 163 c to be selectively connectedtogether. The star connection by the star connection-end moving contacts167 a, 167 b, and 167 c and the delta connection by the deltaconnection-end moving contacts 164 a, 164 b and 164 c are achieved in analternating fashion. For example, the star connection by the starconnection-end moving contacts 167 a, 167 b, and 167 c is achieved whenthe delta connection by the delta connection-end moving contacts 164 a,164 b and 164 c is released.

Return springs 165 are arranged around the star-delta connection-endmoving core 161 between the upper surface of the star-deltaconnection-end electromagnet 140 and the lower surface of the star-deltaconnection-end vertical moving member 162 in order to provide a returnforce for returning the vertical moving member 162 to its originalposition at which the delta connection-end moving contacts 164 a, 164 b,and 164 c are separated from respective associated ones of the fixedcontacts 163 a, 163 b, and 163 c. An arc prevention spring 166 isarranged in the star-delta connection-end vertical moving member 162 inorder to always urge the delta connection-end moving contacts 164 a, 164b, and 164 c and the star connection-end moving contacts 167 a, 167 b,and 167 c toward respective corresponding portions of the fixed contacts163 a, 163 b, and 163 c, thereby increasing the contact force of thedelta connection-end moving contacts 164 a, 164 b, and 164 c or the starconnection-end moving contacts 167 a, 167 b, and 167 c when the deltaconnection-end moving contacts 164 a, 164 b, and 164 c or the starconnection-end moving contacts 167 a, 167 b, and 167 c come into contactwith the fixed contacts 153 a, 153 b, and 153 c, so as to suppressgeneration of arc at those contacts.

A timer 170 is arranged beneath the main circuit-end electromagnet 130and star-delta connection-end electromagnet 140 in the interior of thebody 110. The timer 170 serves to count an activation time of the maincircuit-end electromagnet 130, thereby determining a point of time whenthe star-delta connection-end electromagnet 140 is to be activated.Isolating plates 180 are also arranged to isolate adjacent ones of thepower terminals 121 a, 121 b, and 121 c, adjacent ones of the mainstarting terminals 122 a, 122 b, and 122 c, and adjacent ones of thestar-delta terminals 123 a, 123 b, and 123 c, respectively.

In the drawings, the reference: numeral 191 denotes terminals to whichpower lines are coupled in order to supply current to the coils 132 and142. The reference numeral 192 denotes bolts respectively coupled to theterminals 191 in order to provide an easy connection of the power linesto the terminals 191.

The electromagnetic switch device C for star-delta connections havingthe above mentioned configuration operates in a connection state, asshown in the equivalent circuit diagram of FIG. 4, in such a fashionthat it establishes a star connection, when it is desired to start upthe electric motor M, in order to achieve a start-up of the electricmotor M using starting current and starting torque reduced to a ⅓ levelwhile switching the connection of the electric motor M to a deltaconnection after completion of the start-up of the electric motor M. Forthe best understanding of the present invention, elements of FIG. 4respectively corresponding to those in FIGS. 3a and 3 b are denoted bythe same reference numerals.

Now, the operation of the electromagnetic switch device C for star-deltaconnections according to the present invention will be described.

When current flows through the coil 132 of the main circuit-endelectromagnet 130, which is constructed by the fixed core 131 and thecoil 132, upon starting the three-phase electric motor M, theelectromagnet 130 is magnetized by virtue of the current. Simultaneouslywith the magnetization of the electromagnet 130, the timer 170 begins tocount the activation time of the electromagnet 130.

As the electromagnet 130 is activated, it generates a magnetm/etic . rcegreater than the resilience of the return spring 155, so that the movingcore 151 and vertical moving member 152 are downwardly moved. At thesame time, the main circuit-end moving contacts 154 a, 154 b, and 154 care downwardly moved, so that they come into contact with the maincircuit-end fixed contacts 153 a, 153 b, and 153 c, respectively.

In such an initial state, the star-delta connection-end electromagnet140 is maintained under a non-magnetization condition, that is, acondition in which no current flows through the coil 142. Accordingly,the star-delta connection-end moving coil 161 and star-deltaconnection-end vertical moving member 162 are maintained in a state inwhich they are spaced away from the coil 142 by virtue of the resilienceof the return spring 165. In this state, the delta connection-end movingcontacts 164 a, 164 b, and 164 c are separated from the associated fixedcontacts 163 a, 163 b, and 163 c whereas the star connection-end movingcontacts 167 a, 167 b, and 167 c are in contact with the associatedfixed contacts 163 a, 163 b, and-163 c, that is, in a stateshort-circuited to the associated fixed contacts 163 a, 163 b, and 163c.

Accordingly, the three-phase electric motor M is in a star connectionstate, so that it is started up by electric power supplied via thethree-phase power lines R, S, and T respectively connected to the powerterminal 121 a, 121 b, and 121 c.

After a predetermined period of time elapses, the timer 170 operates toallow current to flow through the coil 142 of the star-deltaconnection-end electromagnet 140. By virtue of the current, thestat-delta connection-end electromagnet 140 is magnetized.

As the electromagnet 130 is activated, it generates a magnetic forcegreater than the resilience of the return spring 165, so that the movingcore 161 and vertical moving member 162 are downwardly moved.

At the same time, the star connection-end moving contacts 167 a, 167 b,and 167 c are downwardly moved, so that they are separated from theassociated fixed contacts 163 a, 163 b, and 163 c, respectively. Also,the delta connection-end moving contacts 164 a, 164 b, and 164 c aredownwardly moved, so that they come into contact with the associatedfixed contacts 163 a, 163 b, and 163 c, respectively.

As a result, the main starting terminals 122 a, 122 b, and 122 c areconnected with the star-delta terminals 123 a, 123 b, and 123 c,respectively, so that the three-phase electric motor M is switched to adelta connection state in which it is driven at a full speed.

INDUSTRIAL APPLICABILITY

As apparent from the above description, the present invention providesan electromagnetic switch device for star-delta connections whichincludes two electromagnets arranged in its body and two switchingng usoperating in accordance with respective magnetization states of theelectromagnets in order to selectively establish a star connection or adelta connection for a three-phase electric motor. The electromagneticswitch device of the present invention can reduce installation costs andan occupation space when it is applied to a star-delta starter. Inaddition, there is no unnecessary wiring. Accordingly, it is possible toreduce erroneous connections and erroneous operations.

Although the preferred embodiments of the invention have been disclosedfor illustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions and substitutions are possible, withoutdeparting from the scope and spirit of the invention as disclosed in theaccompanying claims.

What is claimed is:
 1. An electromagnetic switch device for star-deltaconnections comprising: a body; first through third power terminalsarranged at one side portion of the body on an upper surface of the bodyand respectively connected to three-phase power lines; first throughthird main starting terminals arranged at an intermediate portion of thebody on the upper surface of the body and respectively connected toone-side terminals of a three-phase electric motor; first through thirdstar-delta terminals arranged at the other side portion of the body onthe upper surface of the body and connected to the other-side terminalsof the three-phase electric motor, respectively; a star connection plateset on the upper surface of the body and adapted to connect the firstthrough third star-delta terminals to a star circuit; first throughthird contacts set beneath the star connection plate and adapted toconnect the first through third star-delta terminals to a delta circuit;a timer assembled to the body at a bottom of the body while beingintegral with the body, the timer serving to control a start-up time forthe three-phase motor; an electromagnet for a main circuit and anelectromagnet for star-delta connections each including a fixed core anda coil assembled in the interior of the body, each of the electromagnetsbeing selectively magnetized in accordance with a cooperation of thefixed core and coil thereof; a main circuit switching unit assembled toan upper portion of the body at one side of the body so that it isintegral with the body, the main circuit switching unit serving toselectively connect the first through third power terminals with thefirst through third main terminals, respectively, in accordance with themagnetization of the main circuit-end electromagnet; and a star-deltaconnection switching unit assembled to the upper portion of the body atthe other side of the body so that it is integral with the body, thestar-delta connection switching unit serving to connect the starconnection plate to the first through third star-delta terminals inaccordance with the magnetization of the main circuit-end electromagnetunder a condition in which the first through third power terminals areconnected with the first through third main terminals, thereby allowingthe three-phase motor to be start up in a star connection state, thestar-delta connection switching unit also serving to connect the firstthrough third delta connection contacts to the first through thirdstar-delta terminals when the star-delta connection-end electromagnet ismagnetized in accordance with an operation of the timer after thestart-up of the three-phase motor, thereby causing the three-phase motorto be driven in a delta connection state.
 2. The electromagnetic switchdevice according to claim 1, wherein the star-delta switching unitcomprises: a star-delta connection-end moving core adapted to movevertically in accordance with a magnetization of the star-deltaconnection-end electromagnet; a star-delta connectiona connection-endvermoving member integrally coupled to the star-delta connection-endmoving core and adapted to move vertically along with the star-deltaconnection-end moving core; first through third star connection-endmoving members adapted to move upwardly along with the star-deltaconnection-end vertical moving member in accordance with a magnetizationof the main circuit-end electromagnet under a condition in which thefirst through third main terminals are connected to the first throughthird power thermals, so that they are connected to the first throughthird star-delta terminals while being connected to the star connectionplate, thereby allowing the three-phase electric motor to be started upin the star connection state; and first through third deltaconnection-end moving members adapted to move downwardly along with thestar-delta connection-end vertical moving member when the star-deltaconnection-end electromagnet is magnetized after a time set by the timerelapses, following the start-up of the three-phase electric motor in thestar connection state, so that they are connected to the first throughthird star-delta terminals while being connected to the first throughthird delta connection contacts, thereby causing the three-phaseelectric motor to be driven in the delta connection state.
 3. Theelectromagnetic switch device according to claim 1, wherein thestar-delta switching unit further comprises: star-delta connection-endcompression coil springs adapted to always urge the star-deltaconnection-end vertical moving member to move upwardly, thereby allowingthe three-phase electric motor to be started up in the star connectionstate, the star-delta connection coefficient lower than a magnetic forceof the star-delta connection-end electromagnet to allow the star-deltaconnection-end vertical moving member to move downwardly against theurging force of the star-delta connection-end compression coil springswhen the star-delta connection-end electromagnet is -magnetized, therebycausing the three-phase electric motor to be driven in the deltaconnection state, the star-delta connection-end compression coil springsbeing arranged in pair so that those of each pair are disposed atopposite sides of other star-delta connection-end electromagnet,respectively; and star-delta connection-end damping springs for dampingimpact generated when the first through third star connection-end movingmembers abruptly contact associated contact portions -as the star-deltaconnection-end vertical moving member moves upwardly by virtue of theurging force of the star-delta connection-end compression coil springswhile damping impact generated when the first through third starconnection-end moving members abruptly contact associated fixed contactsas the star-delta connection-end vertical moving member moves upwardlyby virtue of the magnetic force of the star-delta connection-endelectromagnet, force of the star-delta connection-end electromagnet,respectively, the star-delta connection-end damping springs beingarranged in the form of a plurality of sets each including threestar-delta connection-end damping springs.